What I want to achieve, is to return the instance created back to C#,
and
add it to a List.

I can’t do it. Currently, I get an InvalidOperationException: “can’t
convert SharedClasses::SimpleItem into SharedClasses::SimpleItem”

Here’s the code I use to create the Ruby instance:

var engine = Ruby.CreateEngine();
var newItem = engine.Execute(ruby);

I posted a Stack Overflow question for a more complex version of this
problem (this is the simplest case I could distill). Under other
circumstances, I can see that the two instances are the same, except
their
context (one is Default and one is LoadNeither).